An actor slit his throat on stage when the prop knife for his suicide scene turned out to be a real one.

Daniel Hoevels, 30, slumped over with blood pouring from his neck while the audience broke into applause at the "special effect". Police are investigating whether the knife was a mistake or a murder plot. They are questioning the rest of the cast, and backstage hands with access to props; they will also carry out DNA tests.

Things went wrong at Vienna's Burgtheater as Hoevels' character went to "kill himself" in the final scene of Friedrich Schiller's Mary Stuart, about Mary Queen of Scots, on Saturday night

It was only when he did not get up to take a bow that anyone realised something had gone wrong.

Though bleeding profusely, Hoevels survived because the knife missed the carotid artery as it sliced into his neck. Wolfgang Lenz, a doctor who treated him, said: "Just a little bit deeper and he would have been drowning in his own blood."

One officer told Austrian TV news: "The rumours are wild, with some claiming that he was the victim of jealous rival.

"We don't know anything for sure yet; we have to work through everyone."

The knife was reportedly bought at a local shop; one possibility is that the props staff forgot to blunt its blade. "The knife even still had the price tag on it," an investigator said.

After emergency treatment at a hospital, Hoevels declared that the show must go on, and returned to the stage on Sunday night with a bandage tied around his neck, ready to once again meet his mock demise.